The present invention relates to a temperature sensitive electrical element, and more particularly to an electrical element of a vitreous enamel refractory metal oxide having a highly linear resistance to temperature characteristic and a relatively high temperature coefficient of resistance, and a method and material for making the same.
In general, temperature sensitive electrical elements of the vitreous enamel resistor type comprise a substrate having a film of glass and particles of a conductive material embedded in and dispersed throughout the glass film. The elements are made by first forming a mixture of a glass frit and particles of the conductive material. The mixture is applied to substrates and fired at a temperature at which the glass frit softens. Certain vitreous resistors such as those utilizing precious metals and precious metal oxides are made by firing in an oxidizing atmosphere, while other vitreous resistors such as those using refractory metals, and refractory metal borides and nitrides, are formed by firing in a non-oxidizing environment. When cooled, the glass solidifies to form the resistors with a glass film having the conductive particles therein.
In order to provide electrical connections to the elements, it is desirable to provide a conductive termination at each end of their resistance films. Heretofore, as disclosed in U.S. Pat. No. 3,358,362 issued Dec. 19, 1967, terminations for vitreous enamel resistors have been provided by the electroless plating of a film of a metal, such as nickel or copper. However, it has been found that such electroless metal film terminations are not compatible with certain vitreous enamel resistance films. In order to make electrical connections to such resistor films, a precious metal, such as silver, is usually applied by another process.
The electrical temperature sensors which heretofore have been produced have characteristically exhibit a non-linear resistance versus temperature curve, or a linear curve over only a portion of the temperature range of -55.degree. C. to +150.degree. C. required for a wide range temperature sensor. The requirement for carefully selecting only certain sensors from a production batch to provide the desirable properties, and the need for compensating networks result in a higher cost for producing sensors with a linear characteristic. Such elements should also provide relatively high temperature coefficients of resistance.